The detection of various gases is necessary to determine whether it is safe to work in certain conditions. In various industrial work areas, certain explosive gases may be released into the atmosphere that can create a dangerous situation, including for example, various hydrocarbon gases such as cyclohexane, butane, bivinyl, and methane among other gases. Such gases generally will become explosive, and thus dangerous, when the amount of the gas reaches a certain level relative to the amount of oxygen in the air. This ratio between the target gas and oxygen is often expressed as a lower explosive limit level (“LEL level”) of the gas, often denoted “% LEL” as a percentage of the target gas in the atmosphere because the amount of oxygen in air is generally constant. Accordingly, under certain work situations where explosive gases may be present, it is imperative to test for the amount of such gases in the air to avoid a dangerous condition.
Various devices are known to detect such dangerous gases. Certain of the known devices detect such gases by passing light through a volume of gas-air mixture and detecting the attenuation of certain wavelengths of the light. Because different gases absorb different wavelengths of light, one can configure such a device to determine the total amount of such gases in the tested volume based on the amount of absorption of light at the specific wavelengths. Such devices then take the measured amount of the target gas and determine the LEL level based on the known conditions of the standard atmosphere.
U.S. Pat. No. 6,545,278 issued to Mottier et al. describes a device that analyzes a gas-air mixture for dangerous gases via infra-red analysis, corrects for variations in sensor operation due to temperature through saved correction tables, and corrects for pressure variations due to altitude based on saved correction tables. Although such a device as described works well under most conditions, the device, however, does not correct for the effect of certain atmospheric conditions on the measured gas-air mixture and potentially is not precise at certain relatively extreme operation conditions.
For example, in situations of high humidity, the amount of oxygen in the air is lessened because of displacement by the large concentration of water vapor in the air. Similarly, large variations in temperature or pressure can increase the error of some devices, especially in high humidity conditions, because some devices do not include error correction based on changes to the gas-air mixture caused by such atmospheric variations. For example, the device described in U.S. Pat. No. 6,545,278, corrects for temperature induced variations in the operation of the light detectors, but not for measurement changes caused by a change in the gas-air mixture as a result of temperature or humidity variations. Although such measurement variations caused by normal atmospheric variations does not introduce significant error, increased error in such devices due to relatively extreme humidity, temperature, and pressure in certain non-typical atmospheric conditions may result in workers being present in dangerous conditions or may result in unnecessary work stoppages based on false warnings of dangerous conditions.